The present invention relates to x-ray apparatus and, more particularly, to a method and apparatus for rapidly positioning an x-ray film with minimum vibration.
In x-ray apparatus, an x-ray sensitive film is positioned in a line with a target and an x-ray source whereby x-rays from the source are attenuated by the target before impinging on the film to thereby obtain an image of the target. One type of x-ray apparatus is a "spot film" system in which multiple images may be obtained on a single large sheet of x-ray film by blocking the x-rays from selected portions of the film sheet and moving the sheet as needed to various positions.
Such spot film devices commonly involve a table on which a target, e.g., a patient, is positioned and a motor driven mechanism within the table for moving the table to various desired locations. A film holding mechanism is positioned above the patient and also includes a motor for moving the film into selected positions. The actual target may be only a small area of the patient's anatomy. Present day devices include x-ray impervious plates which can be selectively positioned between the patient and film in order to obtain multiple images on a single film. However, if the target area is not changed, the film must be re-positioned in order to align an unexposed portion with the target.
Each time that a film holder or other apparatus mechanically connected to the film holder is moved, whether from an original loading position or merely for re-positioning, translational forces applied to the film holder during starting and stopping create mechanical vibrations within the x-ray apparatus. Such vibrations may be of the film holder or may involve other structural elements of the x-ray table. In either case, the vibrations can result in jitter of the x-ray film and a loss of definition (resolution) or image quality if an exposure is made before the vibrations have ceased. The problem of controlling vibrations is exacerbated since a main objective of the film handling device or holder is to deliver the film to a desired position as rapidly as possible in order to minimize the time required between exposures.
It is an object of the present invention to provide an improved method for positioning a film holder and associated apparatus.
It is another object of the present invention to provide an improved method for positioning a film holder which rapidly transfers film between positions while minimizing mechanical vibration.